Composite material, electrical circuit or electric module

ABSTRACT

The invention relates to a novel composite material, especially for applications in the field of electrical engineering. Said novel material has a thermal coefficient of expansion that is smaller than 12×10 −6  K −1  in at least two axes of a three-dimensional system that are perpendicular in relation to each other.

The invention relates to a composite material or a composite rawmaterial according to the preamble of claim 1 and to an electric circuitor an electric module according to the preamble of claim 32.

A “composite material” or “composite raw material” according to thepresent invention is generally a material comprising several materialcomponents, for example in a common matrix or also at least partially inat least two adjacent material sections that are bonded together.

A “component for thermal dissipation” or a “heat sink” according to theinvention are generally components that are used in electronics andparticularly in power electronics and are used to dissipate heat lossand to cool electric or electronic components, for example base platesand/or thermal dissipation or cooling plates in electric circuits ormodules, substrates for electric or electronic components, housings orhousing elements of electric components or modules, and also, forexample, coolers, heat pipes or elements of such active heat sinksthrough which a coolant flows, such as water.

In many areas of technology, composite materials are used as materialsfor constructions, components, etc., particularly when materialproperties are required that cannot be achieved with a single materialcomponent. The desired properties for the composite material can beoptimized by carefully selecting the individual components and thephysical and/or chemical properties of these components, for example thethermal properties.

“Materials for Thermal Conduction”, Chung et al., Appl. Therm. Eng., 21,(2001) 1593-1605, gives a general overview of materials for thermalconducting or thermal dissipating materials. The article outlines theproperties of possible individual components and relevant examples forthe composite materials.

Ting et al reports in J. Mater. Res., 10 (6), 1995, 1478-1484 on themanufacture of aluminum VGCF (Vapor Grown Carbon Fiber) composites andtheir thermal conducting properties. U.S. Pat. No. 5,814,408 Ting et alis the resulting patent specification for the AL-VGCF MMC.

Composites with Carbon Fibrils™, a defined CVD carbon fiber, in both ametal and polymer matrix are mentioned in U.S. Pat. No. 5,578,543 Hochet al.

Ushijima et al describes in U.S. Pat. No. 6,406,790 the manufacture of acomposite material with a special variant of CVD grown carbon fibers asa filling material by means of pressure infiltration of the matrixmetal.

Houle et al report in U.S. Pat. No. 6,469,381 on a semiconductor elementthat dissipates the heat produced during operation by including carbonfibers in the substrate.

The use of coated carbon fibers in composite materials with a metallicmatrix is described by Bieler et al in U.S. Pat. No. 5,660,923.

Al₂O₃ fibers in an Al matrix and the manufacture of correspondingfiber-reinforced composite materials is described in U.S. Pat. No.6,460,497, McCullough et al.

Due to the improved electrical properties, the use of metal-ceramicsubstrates as printed circuit boards, for example substrates made ofaluminum oxide (Al₂O₃) or increasingly also substrates made of aluminumnitride (AlN) is known in particular for power modules, which areincreasingly being used in electric drive systems, for example intraffic and automation technology. Layers or base plates made of copper,which have high thermal conductivity and therefore are suitable fordissipating power or heat loss and also for thermal spreading, haveheretofore been used for the substrate or transition layer to a heatsink, which often has to dissipate a considerable power loss from such apower module.

The disadvantage of this is the high fluctuation in the thermalexpansion coefficients of the materials used, namely of the ceramic, thecopper and also of the silicon of the active electric or electroniccomponents of such a module. Such power modules and their components aresubjected to a considerable change in temperature not only during themanufacturing process, but also during operation, for example during thetransition from the operating phase to the dwell or not operating phaseand vice versa, and also when the module is switched during operation.Due to the differing expansion coefficients, these temperature changescause mechanical stress in the module, i.e. mechanical stress betweenthe ceramic and the adjacent metallizations or metal layers (such asbase plate on one side of the ceramic layer and strip conductors,contact surfaces, etc. on the other side of the ceramic layer), and alsobetween metal surfaces and the electric or electronic components locatedthereon, in particular semiconductor elements. Frequent mechanicalalternating stress causes material fatigue and therefore failure of themodule or its components.

This problem is compounded by the additional factor of miniaturizationand by the ensuing increase of the power density of power modules. Thethermal expansion coefficients

of the material components of a power module with a copper-ceramicsubstrate are within the range of

=16.8×10⁻⁶K⁻¹ for copper and

=3×10⁻⁶K⁻¹ for silicon.

Reference is also made to the following table, in which the thermalconductivity

and the thermal expansion coefficient

are specified for various materials. □_(th) in W/mK □ in 10⁻⁶/K Ag 42819.7 Cu 395 16.8 CuCo0.2 385 17.7 CuSn0.12 364 17.7 Au 312 14.3 Al 23923.8 BeO 218 8.5 AlN 140-170 2.6 Si 152 2.6 SiC 90 2.6 Ni 81 12.8 Sn 6527 AuSn20 57 15.9 Fe 50 13.2 Si₃N₄ 10-40 3.1 Al₂O₃ 18.8 6.5 FeNi42 15.15.1 Silver epoxy cement 0.8-2   53 Epoxide molding 0.63-0.76 18-30 SiO₂0.1 0.5 W 130 4.5 Mo 140 5.1 Cu/Mo/Cu 194 6.0 AlSiC 160-220  7-10

Since the thermal conductivity for dissipation of the power loss isnecessary, the metals used especially in semiconductor modules or theirsubstrates for the metallizations, the base plate, etc. must be able toconduct heat sufficiently. At present, materials with a copper oraluminum base, such as Cu—W, Cu—Mo or Al—SiC are preferred especiallyfor heat sinks.

The method of manufacturing the metallization required for stripconductors, connections, etc. on a ceramic, for example on analuminum-oxide ceramic, using the direct copper bonding technology isknown in the art, the metallization being formed by metal or copperfoils or metal or copper sheets, featuring on the top side a layer orcoating (melt layer) from a chemical bond with the metal and a reactivegas, preferably oxygen. In the method described for example in U.S. Pat.No. 3,744,120 or in DE-PS 23 19 854, this layer or coating (melt layer)forms a eutectic with a melting temperature below the meltingtemperature of the metal (e.g. copper), so that when the foil is placedon the ceramic and all layers are heated they are bonded together,namely through melting the metal or copper essentially only in the areaof the melt layer or oxide layer.

This DCB method then comprises the following steps:

oxidation of a copper foil in a manner that results in an even copperoxide layer;

placing of the copper foil on the ceramic layer;

heating of this composite or strukture to a process temperature betweenapproximately 1025 and 1083° C., e.g. to approximately 1071° C.;

cooling to room temperature.

The object of the invention is to provide a composite material, whichwhile maintaining a high degree of thermal conductivity, which isgreater than or at least equal to that of copper or copper alloys, has athermal expansion coefficient significantly lower than that of copper.This object is achieved by a composite material according to claim 1. Anelectric circuit or an electric module is exemplified according to claim32.

The composite material according to the invention, which is suitable forexample for electrical engineering applications and therefore forapplications as a substrate or as a component for dissipating heat inelectric power modules, consists therefore essentially of three maincomponents, namely of at least one metal or at least one metal alloy, ofat least one ceramic and of nanofibers, which have a thickness between1.3 nm and 300 nm, and the length/thickness ratio for a majority of thenanofibers contained in the composite material being greater than 10.The ceramic content can be replaced partially or entirely by glass, forexample by silicon oxide.

The nanofibers used effect the desired reduction of the thermalexpansion coefficient of the composite material in at least twoperpendicular spatial axes, preferably in all three perpendicularspatial axes.

In the embodiment of the composite material according to the invention,the following measures are possible in further embodiments of theinvention:

The nanofibers are distributed isotropically in their orientation atleast in the at least two spatial axes.

At least some of the nanofibers are for example nanotubes, which areespecially stable in axial direction, so that they contribute veryeffectively to the desired reduction of the thermal expansioncoefficient.

The nanofibers preferably are made of an electrically conductivematerial, so that the composite material comprising the nanofibers orthe part of the composite material comprising the nanofibers can also beused for electric strip conductors or contacts, etc., i.e. it possessesthe necessary electric conductivity for this application.

The nanofibers are preferably such made of carbon and/or of boronnitride and/or of tungsten carbide. Other materials or composites thatare suitable for the manufacture of nanofibers are also conceivable, inparticular nanofibers made of carbon and coated with boron nitrideand/or tungsten carbide.

The ceramic used for the composite material according to the inventionis preferably an aluminum oxide ceramic or an aluminum nitride ceramic,in which case the aluminum nitride ceramic is characterized byespecially high electric strength and by increased thermal conductivity.

The metal component used for the invention is preferably copper or acopper alloy. This applies in particular in the event that the compositematerial is to be used for substrates or printed circuit boards or as acomponent for thermal dissipation in electric circuits or modules.Copper, and also copper alloys, are relatively easy to process, inparticular when this material component of the composite materialcontains the nanofibers.

It is also possible to provide the nanofibers in the at least one metalor the at least one metal alloy and/or in the ceramic and/or in theglass, for example in a matrix formed by the metal or metal alloy.

The nanofiber content of the composite material is for example between10 and 70 percent by volume, preferably between 40 and 70 percent byvolume, in relation to the total volume of the material component of thecomposite material containing said fibers.

If the nanofibers are contained in the metal or in the metal alloy ofthe composite material, then a wide range of methods are available forimplementing this special design. It is possible, for example, to firstform a perform from the nanofibers, for example in the form of athree-dimensional latticework, a fleece-like structure, a hollow body ortubular structure, etc., wherein the at least one metal or the at leastone metal alloy is incorporated into this perform. A wide variety ofmethods is conceivable for this design in particular, for examplethrough chemical and/or electrolytic precipitation, through meltinfiltration, etc.

According to one embodiment of the invention, the composite material isa fiber-reinforced ceramic-glass composite as a substrate for electricor electronic applications and consists of a carrier substrate based onceramic and/or glass materials and at least one fiber-reinforced metallayer applied to one side. The fibers in the metal layer are then forexample carbon nanotubes, with a thickness of 1.3 to 300 nm and alength/thickness ratio >10, and the nanofibers are present in the metalmatrix of the metal layer with a content of 10 to 70 percent by volume.If the carrier substrate also contains nanofibers, then they have a highnitride and/or tungsten carbide content.

Furthermore, it is possible to apply the metal and the nanofibers to aperform or a substrate made of metal and/or ceramic, for example throughchemical and/or electrolytic precipitation.

Other methods for manufacturing the matrix of the at least one metal orthe at least one metal alloy with the nanofibers are conceivable, forexample, the so-called HIP technology, in which the at least one metalor the at least one metal alloy is inserted into a capsule in powderform mixed with the nanofibers, after which the capsule is tightlysealed with a cap. Afterwards, the interior of the capsule is evacuatedand sealed so that it is gastight. Then pressure is applied to theentire capsule (e.g. gas pressure using inert gas, for example argon, orhydrostatic pressure) and therefore also to the material contained inthe capsule, while simultaneously heating it to a process temperaturebetween 500 and 1000° C.

In a further process step, after cooling, the capsule and the metalblank containing the nanofibers are separated, so that the blank can befurther processed, for example through machining or cutting, sawingand/or rolling to manufacture boards or foils, which then are bondedwith a ceramic layer to manufacture a metal-ceramic substrate or aprinted circuit board.

Especially for use in electric or electronic components the compositematerial according to the invention is designed as a laminate, namelywith at least two bonded material sections or layers, where one materialsection or one layer is made of the at least one metal or the at leastone metal alloy and the other material section or the other layer ismade of ceramic. The nanofibers are then contained for example in the atleast one material section made of the metal or the metal alloy.Generally it is also possible that the nanofibers are likewise containedin the ceramic, for example to reinforce the mechanical stability of theceramic and/or to improve the thermal conductivity of the ceramic.

If the composite material consists of at least one material section madeof the at least one metal or the at least one metal alloy and of thematerial section made of ceramic, then both material sections or layersare bonded together, for example by soldering, preferably by the activesoldering process, or using the known direct bonding technology.

Especially in the possible embodiment of the composite material as ametal-ceramic substrate or printed circuit board, a metallization isprovided on at least one surface of one ceramic layer, which(metallization) is formed by the at least one metal or the at least onemetal alloy and contains the nanofibers. This metal layer is then forexample the base plate of such a substrate or is bonded with such a baseplate, with which the substrate is bonded with a passive heat sink, forexample in the form of a cooler body or with an active heat sink, forexample in the form of a cooler through which a coolant flows, also amicro cooler.

Strip conductors and/or contact surfaces and/or fixing or fasteningsurfaces for components of an electric circuit or module, for example,are then provided on the other surface of the ceramic layer. The metalor metal alloy forming these strip conductors, contact surfaces, etc.can also contain the nanofibers, in which case the structuredmetallization of the strip conductors etc. is effected in the normalmanner, namely in that after application of a metal layer, this layer isformed into the structured metallization, for example through anetch-masking process.

Therefore, the invention is used to create a composite material in whichconsiderably higher conductivity (e.g. >380 W(mK)⁻¹) is achieved throughthe dispersion of the nanofibers into the metal matrix, for examplecopper matrix, combined with reduced thermal expansion. Furthermore,especially the use of copper for the metal matrix ensures easyprocessing of the metal containing the nanofibers, so that all standardprocessing methods, such as drilling, milling, punching, and alsochemical processing, are possible.

The composite material according to the invention can be used forsolutions in the field of thermal management that previously presentedmajor difficulties, e.g. also in laser technology, where in particularthe differing thermal expansion coefficients between the semiconductormaterial of a laser bar and the metal of a heat sink considerablydecreases the service life of laser diodes or laser diode arrays. Theimproved thermal conductivity can be used to achieve higher powerdensities than previously possible in electric and electronic powermodules, namely with the possibility of miniaturization of electricaland electronic modules and assemblies and with the possibility ofadditional applications especially also in such technical fields inwhich the miniaturization and ensuing reduction of mass and weight is ofconsequence, as in air and space technology.

The composite material according to the invention makes it possible tocombine in one material properties that were previously less thanoptimally compatible. If the nanofibers are provided in the metalmatrix, then they serve as reinforcing components, which, with theirhigh thermal conductivity (greater than 1000 W(mK)⁻¹) and theirnegligible thermal expansion coefficient, significantly reduce theexpansion coefficient of the overall composite material and Improve itsthermal conductivity.

The invention is described below in detail based on exemplaryembodiments with reference to the drawings, wherein:

FIG. 1 shows a simplified representation of an electric power modulewith a composite material according to the invention;

FIG. 2 shows a simplified schematic representation of the variousprocess steps (positions a-d) of the HIP process for manufacturing ametal-nanofiber composite;

FIG. 3 shows a schematic representation of a process for furtherprocessing of starting material containing the at least one metal or theat least one metal alloy and the nanofibers;

FIGS. 4 and 5 show a schematic representation in side view and in topview of a bath for electrolytic and/or chemical co-precipitation ofmetal and nanofibers on a metal foil or perform;

FIGS. 6 and 7 show a schematic representation in top view of a bath forelectrolytic and/or chemical co-precipitation of metal on a performformed by nanofibers.

FIG. 1 shows a simplified representation in side view of an electricpower module 1, which consists, inter alia, of a ceramic-coppersubstrate 2 with various electronic semiconductor components 3, of whichonly one power component is depicted for the sake of clarity, and of abase plate 4. The copper-ceramic substrate 2 comprises a ceramic layer5, for example of aluminum oxide or aluminum nitride ceramic, whereindifferent ceramics can be used if the layer 5 is formed from multipleparts, and one upper metallization 6 and one lower metallization 7. Themetallizations 6 and 7 in the depicted embodiment are each formed by afoil, which contains nanofibers in a matrix of copper or a copper alloy,for example with a content of 10-70 percent by volume, in relation tothe total volume of the respective foil or metallization, preferablywith a content of 40-70 percent by volume.

The component 3 is a power semiconductor component, e.g. a transistorfor switching high currents, e.g. for controlling an electric motor or adrive. Other power semiconductor components are also conceivable, forexample laser diodes. The thickness of the base plate 4 in the axisdirection perpendicular to the planes of the metallizations 6 and 7 is amultiple of the thickness of the foils used for these metallizations 6and 7.

The two metallizations 6 and 7 are bonded two-dimensionally with onesurface of the ceramic layer 5 using a suitable method, for example bymeans of DCB technology or the active soldering process. Furthermore,the metallization 6 is structured in the required manner, preferablyusing the etch-masking method known to persons skilled in the art, inorder to form strip conductors, contact surfaces, fasting surfaces forfastening or soldering of components 3, of shielding surfaces or stripsfunctioning as inductors, etc. Other methods are also conceivable, forexample in the manner that the structuring is produced by mechanicalprocessing of the foil forming the metallization 6, for examplefollowing or preceding the application of the metallization 6 to theceramic layer 5. The foil forming the metallization 7 is not structuredin the depicted embodiment. In the depicted embodiment, this foil coversa large part of the bottom of the ceramic layer 5, wherein the edge areaof the ceramic layer 5 is kept free from the metallization 7 in order toincrease the electric strength, i.e. the edge of the metallization 7ends at a distance from the edge of the ceramic layer 5. Furthermore,the base plate 4 in the depicted embodiment is designed so that itsperimeter clearly protrudes beyond the perimeter of the copper-ceramicsubstrate 2. The base plate 4 is for example the base plate of a housingof the power module not further depicted.

The metallization 7 is connected two-dimensionally on its surface facingaway from the ceramic layer 5 with the base plate 4, using a suitablemethod, such as soldering, brazing or active soldering, or likewiseusing DCB technology. The base plate 4 in the depicted embodiment islikewise made of a metal or a metal alloy, for example of copper or acopper alloy, wherein the metal or the metal alloy of the base plate 4likewise contains the nanofibers with a content of 10-70 percent byvolume relative to the total volume of the base plate 4, preferably witha content of 40-70 percent by volume. The nanofibers in themetallizations 6 and 7 and in the base plate 4 are distributedisotropically or nearly isotropically with respect to their orientationat least in the two perpendicular spatial axes that define the planes ofthe metallizations 6 and 7 and the plane of the top of the base plate 4connected with the metallization 7.

The nanofibers have a thickness between 1.3 nm and 300 nm, wherein thegreater part of the nanofibers contained in the metal matrix has alength/thickness ratio>10. The nanofibers in this embodiment have acarbon base or are made of carbon, for example in the form of nanotubes.Generally it is also possible, however, to replace these nanofibers madeof carbon in whole or in part with nanofibers made of another suitablematerial, for example of boron nitride and/or tungsten carbide.Generally the nanofibers can be distributed Isotropically with respectto their orientation in all three perpendicular spatial axes, i.e. inthe two axes defining the planes of the metallizations 6 and 7 and thetop of the base plate 4 and in the axis extending perpendicular to theother two axes.

The use of nanofibers in the matrix of the metal or metal alloysignificantly reduces the thermal expansion coefficients of themetallizations 6 and 7 and in particular also of the base plate 4,especially in the axes of the preferred orientation of the nanofibers,namely in the axes defining the planes of the metallizations and theplanes of the top of the base plate, to a value of <5×10⁻⁶K⁻¹,especially also in the relevant temperature range for substrates ofsemiconductor modules, i.e. between room temperature (approximately 20°C.) and 250° C. The electric conductivity especially of the stripconductors formed by the metallization 6 corresponds to the electricconductivity of copper or of a copper alloy without the nanofibers.

The thermal conductivity

of the metallizations 6 and 7 and of the base plate 4 is greater thanthat of copper and is for example on the order of

=600 W(mK)⁻¹ or greater. Due to the extremely reduced thermal expansioncoefficient

as compared with pure copper or a copper alloy, it is clearly adapted tothe thermal expansion coefficient of the silicon of the semiconductorcomponent 3, and also clearly adapted to the thermal expansioncoefficient of the ceramic of the ceramic layer 5. This significantlyreduces thermal stress, as a result of temperature changes in the powermodule 1, between the metallization 6 and the silicon body of thecomponents 3 and the ceramic of the ceramic layer 5, and in particularalso thermal stress between the metallization 7 reinforced by the baseplate 4 and the ceramic layer 5. Such temperature changes are caused bythe switching states of the power module 1, and also by changes in powerduring operation of the power module, for example by correspondingcontrol of this module.

The improved thermal conductivity as compared with copper significantlyimproves the thermal dissipation of the heat loss produced by thesemiconductor component 3 and also significantly improves the thermalspreading through the metallization 7 and improves the transfer of thepower loss to the base plate 4. The latter is then connected with apassive heat sink, for example with a cooler or radiator, which islocated in a current of a medium dissipating the heat loss, in thesimplest case an air current, or the base plate 4 is connected to anactive heat sink, for example with a micro cooler, through which acoolant flows, for example a gaseous and/or vaporous and/or liquidcoolant, for example water. Furthermore it is possible to provide thebase plate 4 on a so-called heat pipe for the especially effectivedissipation of the heat loss from this base plate 4 to a passive oractive cooler.

As an alternative to the embodiments described above, it is alsopossible to design the base plate 4 as a cooler, in particular as anactive cooler, e.g. micro cooler, through which the coolant flows, oralso as a heat pipe. In these cases it is also advantageous tomanufacture a part of the cooler or heat pipe, which (part) is connectedto the metallization 7, from the metal containing the nanofibers or fromthe corresponding metal alloy.

FIG. 2 shows, in various process steps (positions a-d), a possibilityfor manufacturing a starter material consisting of the metal matrix andthe nanofibers contained in this matrix. In this method, which is alsoreferred to as the HIP method, a powdered mixture 8 of particles fromthe metal or metal alloy, for example of copper or copper alloy, and ofthe nanofibers are inserted into a capsule 9, so that this capsule 8 isfilled to approximately 60% of its volume with the mixture 8.

Mixing additives can also be added to the mixture 8, especially in orderto maximize the portion of nanofibers and to achieve an evendistribution of these fibers, inter alia, to reduce the adhesion betweenthe nanofibers. Furthermore, to improve the bond between the metal, forexample copper, and the carbon of the nanofibers, it can be advantageousto use nanofibers with a fishbone surface structure, which improves themechanical bond. It can also be advantageous to coat the nanofibers withreactive elements, which cause a chemical bond, and/or to charge thenanofibers with the metal and/or with ceramic and/or boron nitrideand/or tungsten carbide, for example by means of vapor deposition, forexample.

In a further process step (position b) a cap 10 is placed on the upperopening of the capsule 9 and is bonded tightly with the capsule, forexample by welding.

In a further process step, the interior of the capsule 9 is evacuated bymeans of a connection 11 provided on the cap 10 and the interior of thecapsule 8 is then sealed so that it is gastight.

In a further process step (position d) the ductile, sealed capsule 9 issubjected to high pressure on all sides at a process temperature between500 and 1,000° C., for example. This pressurization on all sides of thecapsule 9 takes place in a closed chamber 12 by means of hydrostaticpressure acting on the capsule 9, as indicated in position d by thearrows there. This actual HIP process causes a reduction in volume,resulting in deformation of the capsule 9. As a rule, the loss of volumeoccurring during this deformation is approximately 5-10%, but can alsobe greater, for example as high as 20%. The capsule 9 and thecorresponding cap 10 and the connection between these two elements issuch that the capsule is not damaged. In order to calculate thereduction behavior, the capsule 9 has a simple geometric shape and thinwalls.

After the HIP process, the capsule 9 and the starter materialmanufactured for example as a block in the HIP process are separated, sothat the starter material can be further processed in a suitable manner.

The capsule 9 and its cap 10 serve several functions in the HIP process,namely as an enclosed space during the evacuation for reduction of theopen porosity in the powdered starter material, for transfer of thehydrostatic pressure during the actual HIP process and also for shapingthe end product produced by the method.

FIG. 3 shows, in various positions a-d, a possibility for furtherprocessing of the end product 13 produced by the HIP process. This isdepicted as a block in FIG. 3 (position a). Using a suitable rollermechanism 14 the product 13 is then formed into a foil 15 (position b),which is then rolled for further use (position c). Position d againshows that the foil 15 or corresponding blanks from this foil can beapplied, for example using the DCB method or another suitable process,to the ceramic layer 5 in order to form the metallizations 6 and 7, inwhich case the metallization 6 is structured in further process stepsnot depicted in FIG. 3.

FIGS. 4 and 5 show a further possibility for manufacturing the starteror row material, which contains the nanofibers in the metal matrix. Inthis process, metal or copper foils are arranged in a suitable bathcontaining the nanofibers and the metal, for example copper, from which(bath) copper and nanofibers are then precipitated electrolyticallyand/or chemically onto the foil blanks 16.

The starter material obtained from this process is then used directly asa layer containing the metal or metal alloy together with the nanofibersin a laminated embodiment of the composite material according to theinvention, for example for the metallizations 6 and 7 or the base plate4 of the power module 1 of FIG. 1, or the (plate-shaped) startermaterial produced with this process is subjected to further processing,for example rolling, before it is used as a material component in thecomposite material.

In deviation from the above description, it is possible in the processof FIGS. 4 and 5 to provide one or more performs in the bath 17, theperform being formed by a three-dimensional structure, for example anetwork or a fleece-like structure made of nanofibers, so that theprecipitation of copper and additional nanofibers from the bath 17 takesplace on the respective perform to form a material containing thenanofibers and the metal or copper. For better bonding with the metal,the nanofibers of the perform in this embodiment are also chemicallypretreated with reactive elements, which improve the mechanical bondbetween the nanofibers and the metal, for example copper. The chargingof the nanofibers with the metal, for example by means of vapordeposition, Is likewise conceivable in this process.

For the perform in the process in FIGS. 4 and 5, the ceramic layer 5itself can also be used, on which the metal (copper) and the nanofibersare then precipitated electrolytically and/or chemically from the bath17. For this purpose, the ceramic layer 5 is first pretreated on itssurfaces, on which the co-precipitation of nanofibers and metal is totake place, for example electrically conductive, e.g. by applying a thinmetal or copper layer.

FIGS. 6 and 7 show as a further possible embodiment a process in whichcopper is electrolytically and/or chemically precipitated on performs18, which are formed by interlocked fibers, from a bath 19, whichcontains coppers or copper salts. The product thus obtained can then beused as the starter material for further processing. Furthermore, inparticular with this embodiment it is also possible to allow nanofibersor copper-coated nanofibers to protrude from the material containingthem, resulting in an impurity resistant lotus effect and/or enablingcontrol of wetting effects of the material.

The invention was described above based on exemplary embodiments. Itgoes without saying that numerous modifications and variations arepossible without abandoning the underlying inventive idea on which theinvention is based.

For example, it is possible with the power module 1 of FIG. 1 tomanufacture only the base plate 4 and/or only one of the metallizations6 or 7 from the material containing the nanofibers. Furthermore, it isalso possible to provide nanofibers in the ceramic layer 5, in order toincrease the thermal conductivity of the ceramic layer, for example.

REFERENCE NUMBERS

-   1 power module-   2 copper-ceramic substrate-   3 power component-   4 base plate-   5 ceramic layer-   6, 7 metallization-   8 mixture-   9 capsule-   10 cap-   11 cap connection-   12 chamber-   13 starting product of metal matrix with nanofibers-   14 rolling mechanism-   15 foil-   16 starter foil-   17 bath for co-precipitation of nanofibers and copper-   18 perform-   19 bath for precipitation of copper

1. A composite material or composite raw material, comprising: a matrixof at least one metal or metal alloy, at least one ceramic and/or oneglass and nanofibers with a thickness between approximately 1.3 nm to300 nm, with a length/thickness ratio for the most part greater
 10. 2. Acomposite material according to claim 1, wherein if the compositematerial is embodied as a fiber-reinforced metal-ceramic-glass compositematerial as a substrate for electric applications for thermalmanagement, consisting of a carrier substrate based on ceramic or glassmaterials and of at least one fiber-reinforced metal layer applied onone side, the fibers in the metal layer consist of carbon nanotubes,which have a thickness of 1.3 to 300 nm and a length/thickness ratio ofgreater 10, and the content of nanofibers in the metal matrix is between10 and 70 percent by volume.
 3. A composite material according to claim2, wherein the carrier substrate contains nanofibers made of boronnitride and/or tungsten carbide.
 4. A composite material according toclaim 1 wherein the thermal expansion coefficient of the material in atleast two perpendicular spatial axes is less than 12×10⁻⁶K⁻¹, and/or thethermal conductivity of the composite material at least in a partialarea is greater than that of the metal or metal alloy.
 5. A compositematerial according to claim 1, wherein the thermal conductivity of thecomposite material at least in a partial area is greater than that ofcopper.
 6. A composite material according to claim 1, wherein thenanofibers are distributed isotropically or nearly isotropically intheir orientation at least in the at least two spatial axes.
 7. Acomposite material according to claim 1, wherein at least part of thenanofibers are nanotubes.
 8. A composite material according to claim 1,wherein the nanofibers are made of an electrically conductive material.9. A composite material according to claim 1, wherein the nanofibers aremade of carbon and/or boron nitride and/or tungsten carbide.
 10. Acomposite material according to claim 1, wherein the ceramic is made ofaluminum nitride and/or aluminum oxide and/or silicon nitride.
 11. Acomposite material according to claim 1, wherein the metal is copper ora copper alloy.
 12. A composite material according to claim 1, whereinthe metal is aluminum or an aluminum alloy.
 13. A composite materialaccording to claim 1, wherein the nanofibers are provided in a matrixformed by the at least one metal or the at least one metal alloy.
 14. Acomposite material according to claim 1, wherein the nanofibers areprovided in the ceramic and/or in the glass.
 15. A composite materialaccording to claim 1, wherein ceramic particles and nanofibers areprovided in the matrix formed by the at least one metal or the at leastone metal alloy.
 16. A composite material according to claim 1, whereinthe content of the nanofibers in the matrix of the at least one metal ormetal alloy is approximately 10-70 percent by volume.
 17. A compositematerial according to claim 1, further comprising a perform made of thenanofibers, into which the at least one metal or metal alloy is appliedthrough melt infiltration.
 18. A composite material according to claim1, wherein the matrix of the at least one metal or the at least onemetal alloy with the nanofibers is produced using an HIP process.
 19. Acomposite material according to claim 1, wherein the matrix of the atleast one metal or the at least one metal alloy and the nanofibers isproduced through electrolytic and/or chemical precipitation of the metalor of the metal alloy on the nanofibers or a perform made of thenanofibers.
 20. A composite material according to claim 1, wherein thematrix of the at least one metal or the at least one metal alloy and thenanofibers is produced through electrolytic and/or chemicalprecipitation of the metal or of the metal alloy and the nanofibers on aperform made of metal or a metal alloy or of ceramic.
 21. A compositematerial according to claim 1, further comprising its embodiment as alaminate with at least two interconnected material sections or layersforming said laminate.
 22. A composite material according to claim 21,wherein at least one material section is made of ceramic, and at leastone additional material section is made of the at least one metal or theat least one metal alloy.
 23. A composite material according to claim22, wherein the at least one material section made of ceramic containsthe nanofibers.
 24. A composite material according to claim 22, whereinthe at least one material section made of the at least one metal or ofthe at least one metal alloy contains the nanofibers.
 25. A compositematerial according to claim 22, wherein the material sections are bondedtogether by soldering, for example by the active soldering process. 26.A composite material according to claim 22, wherein the materialsections are bonded together by direct bonding, for example by the DCBprocess.
 27. A composite material according to claim 22, wherein thematerial sections are bonded together by adhesive bonding.
 28. Acomposite material according to claim 22, wherein the material sectionmade of the at least one metal or of the at least one metal alloycomprises several elements or several layers.
 29. A composite materialaccording to claim 1, further comprising its embodiment as aceramic-metal substrate or as a printed circuit board with at least oneinsulating layer formed by the ceramic and with at least onemetallization or metal layer formed by the metal or metal alloy on atleast one surface of the ceramic layer, wherein the metal or the metalalloy and/or the ceramic contains the nanofibers.
 30. A compositematerial according to claim 29, wherein the metallization forms stripconductors and/or contact surfaces and/or fastening surfaces on at leastone surface of the ceramic layer.
 31. A composite material according toclaim 30, wherein the metal layer is structured in order to form thestrip conductors and/or contact surfaces and/or fastening surfaces. 32.A composite material according to claim 29, wherein the at least onemetallization or metal layer is connected with an additional elementmade of metal or of the metal alloy, and that the additional elementcontains the nanofibers.
 33. A composite material according to claim 1,further comprising its embodiment as a component for thermaldissipation, as a heat sink or as a housing or as part of a housing. 34.Electric circuit or electric module with at least one substrate and withat least one electric component, wherein the substrate consists at leastpartially of a composite material according to one of the foregoingclaims.